The present invention relates to mechanically strong absorbent materials. More particularly such materials comprise at least one hydrophilic elastomeric fibrous component (HEFC) and at least one absorbent component. Additionally, some embodiments can further comprise an adhesive component. The HEFC can comprise a block copolymer wherein the blocks comprise an elastomeric block and a hydrophilic block. Alternatively, the HEFC can comprise a mixture or solid solution of hydrophilic polymer and elastomeric polymer. The absorbent component is generally in physical proximity to the HEFC resulting in fluid communication therewith. In general, the system operates in the following manner: the HEFC absorbs a liquid and transfers it to the absorbent component where the fluid remains entrapped and/or bound. Embodiments that also include an adhesive component can be fixed in place at a locus where liquid is to be absorbed.
A variety of methods are known in the textile field for creating fibers compatible with the present invention. Melt-blowing, nanofibers-by-gas-jet (NGJ), and electrospinning are non-limiting examples of these techniques. In a melt-blowing process, a stream of molten polymer or other fiber-forming material is typically extruded into a jet of gas to form fibers. The resulting fibers are typically greater than 1,000 nanometers in diameter, and more typically, greater than 10,000 nanometers in diameter. A technique and apparatus for forming fibers having a diameter of less than 3,000 nanometers according to the NGJ technique is described in U.S. Pat. Nos. 6,382,526 and 6,520,425, and these patents are hereby incorporated by reference in their entireties. Here, as well as throughout this application, when an inconsistency exists between the present application and documents incorporated by reference the present application controls.
The electrospinning, (i.e. electrostatic spinning), of liquids and/or solutions capable of forming fibers is well known in the art. Electrospinning has been described in a number of patents as well as in scientific literature. The process of electrospinning generally involves creating an electric field at the surface of a liquid. The resulting electrical forces create a jet of liquid that carries an electric charge. Thus, the liquid jets can be attracted to other electrically charged objects having a suitable electrical potential. As the jet of liquid elongates and travels, the fiber-forming material within the liquid jet dries and hardens. Hardening and drying of the elongated liquid jet can be caused by a variety of means including, without limitation, cooling the liquid; solvent evaporation (i.e. physically induced hardening); or by a curing mechanism (i.e. chemically induced hardening). The resulting charged fibers are collected on a suitably located, oppositely charged receiver and subsequently removed from it as needed, or directly applied to an oppositely charged or grounded generalized target area.
Fibers produced by this process have been used in a wide variety of applications, and are known, from U.S. Pat. No. 4,043,331 to be particularly useful in forming non-woven mats suitable for use in wound dressings. One of the major advantages of using electrospun fibers in wound dressings, is that very thin fibers can be produced having diameters, usually on the order of about 50 nanometers to about 25 microns, and more advantageously, on the order of about 50 nanometers to about 5 microns. These fibers can be collected and formed into non-woven mats of any desired shape and thickness. It will be appreciated that a mat with very small interstices and high surface area per unit mass can be produced because of the very small diameter of the fibers.
Medical dressings formed using non-woven mats of these polymeric fibers can provide particular benefits that depend upon the type of polymer or polymers used, as disclosed by U.S. Pat. No. 4,043,331. A water-wettable or hydrophilic polymer, e.g. a polyurethane, can be used. Alternatively, a polymer that is not water-wettable, or that is at least weakly hydrophobic, e.g. a saturated polyester, can be employed. Where the dressing is formed from a wettable polymer, blood or serum escaping from the wound tends to penetrate the dressing and the high surface area encourages clotting. Such dressings can be used as emergency dressings to halt bleeding. On the other hand, where the dressing is formed from a non-wetting polymer, and where the interstices between the fibers are sufficiently small, i.e., on the order of less than about 100 nanometers, tissue fluids, including blood, tend not to permeate the dressing. Consequently, the fluids are retained adjacent to the wound where clotting will occur. Subsequent removal of such a dressing is facilitated by the absence of blood clots permeating the dressing material. Still further, U.S. Pat. No. 4,043,331 suggests that such dressings have the advantage that they are usually sufficiently porous to allow interchange of oxygen and water vapor between the atmosphere and the surface of the wound.
Besides providing variability as to the diameter of the fibers or the shape, thickness, or porosity of any non-woven mat produced therefrom, the ability to electrospin the fibers also allows for controlled variations in the composition of the fibers, their density of deposition and their inherent strength. The above-identified U.S. patent indicates that it is also possible to post-treat the non-woven mats with other materials to modify their properties. For example, one could increase the strength of the mat using an appropriate binder or increase water resistance by post-treating the mat with silicone or other water-resistant material, such as perfluoro alkyl methacrylate. Alternatively, strength can be increased by utilizing fibers of polytetrafluoroethylene (PTFE).
By varying the composition of the fibers being formed, fibers having different physical or chemical properties can be obtained. This can be accomplished either by spinning a liquid containing a plurality of components, each of which can contribute a desired characteristic to the finished product, or by simultaneously spinning, from multiple liquid sources, fibers of different compositions that are then simultaneously deposited to form a mat. It is also known in the prior art that molecules, particles, and droplets can be incorporated into electrospun nanofibers during the electrospinning process. The resulting mat, of course, would consist of intimately intermingled fibers of different materials.
Ordinarily, wetting the fibrous article compromises strength. This is especially problematic in applications such as diapers, tampons, and the like inasmuch as these applications require both strength and absorbency. Existing patents and printed publications disclose various solutions to this absorption problem, but each is distinguishable from the present invention as will become clear herein.
For instance, one option available in the art is to produce a mat having a plurality of fibrous layers of different materials. For example, wettable and non-wettable polymers offer differing properties. Wettable polymers tend to be highly absorbent but provide mats that are relatively weak, while non-wetting polymers tend to be non-absorbent but provide relatively strong mats. The wettable polymer layer or layers contribute a relatively high level of absorbency to the article while the non-wetting polymer layer or layers contribute a relatively high level of strength. Use of such layering structures, suffers from the disadvantage that the hydrophobic layer can form a barrier to liquids and interfere with the absorption of liquid by the wettable layer. Additionally, upon absorption of liquid, the wettable polymer layer will weaken and misalignment, slipping, or even separation of the layers can occur, possibly resulting in structural failure of the article.
U.S. Pat. No. 4,043,331 suggests that strong, non-woven mats comprising a plurality of fibers of organic, namely polymeric, material can be produced by electrostatically spinning the fibers from a liquid consisting of the material or its precursor. These fibers are collected on a suitably charged receiver. The mats or linings formed on the receiver can then be transferred and used alone or in conjunction with other previously constructed components such as, for example, mats of woven fibers and backing layers to provide a wound dressing having desired characteristics. For instance, in producing wound dressings, additional supports or reinforcement such as mats or linings of fibers, or backing layers can be required in order to adhere the wound dressing to the skin and to provide other desirable properties to the wound dressing. As an example, a mat or lining of non-woven fibers can contain materials having antiseptic or wound-healing properties. Surface treatments of the already formed non-woven mats can also provide added benefits in the production of such wound dressings. However, U.S. Pat. No. 4,043,331 does not provide a medical dressing that adheres to undamaged skin only. It also does not provide a single-component dressing that can adhere to a desired area of a patient, or a dressing comprised of composite fibers that vary in their composition along their length.
It has also been described in PCT International Publication No. WO98/03267 to electrostatically spin a wound dressing in place over a wound. In such a use, the body itself is grounded and acts as a collector of the electrospun fibers. This method of synthesizing a wound dressing allows for solution of some of the problems associated with bandage and gauze storage and preparation. It is well known for example, that gauze and bandages must be stored and maintained in a sterile environment in order to offer the greatest protection in healing wounds. If the gauze or bandages are not sterile, these products offer little help in protecting the wound. Electrospinning a wound dressing in place, over a wound, from a sterile liquid, eliminates these problems.
International Publication No. WO 01/27365, the disclosure of which is incorporated herein by reference in its entirety, describes an electrospun fiber containing a substantially homogeneous mixture of a hydrophilic polymer, a polymer that is at least weakly hydrophobic, and optionally, a pH adjusting compound. The fibers can be deposited directly on their intended usage area without first applying the fibers to a transient, charged receiver or subjecting it to other intermediate fabrication steps. The resulting fibers, however, do not provide a dressing that adheres only to undamaged skin.
International patent application WO 2005/016205 provides an absorbent core made from a matrix of fibers wherein the matrix is reinforced with a stretchable reinforcing member such as scrim, wherein the fibers are anchored to the reinforcing member. This differs from the present invention in part because the reinforcing member and fiber matrix are wholly separate components. In contrast, the present invention is self-reinforcing in the sense that it incorporates hydrophilic character and elastomeric character in a single fibrous mat. The strength of the fibrous mat of the present invention does not depend on anchoring to a separate body such as a scrim. Moreover, the '205 publication does not disclose the use of an absorbent component separate from the fibrous component as does the present invention.
Thus, there is a need in the art for an absorbent, liquid-entrapping, device comprising a hydrophilic elastomeric fibrous component in physical proximity to an absorbent component resulting in fluid communication therewith. Furthermore, there is a need for such an arrangement wherein one or more liquids enter the fibrous component, which transmits the liquids to the absorbent component thereby entrapping the liquids.